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Modeling, Simulation, and Configuration Improvement of Horizontal Ammonia Synthesis Reactor

  • Foad Farivar and Habib Ale Ebrahim EMAIL logo

Abstract

In this work, one-dimensional heterogeneous model has been developed for an intercooled horizontal ammonia synthesis reactor (HASR) of the Khorasan petrochemical plant. The model is further extended to simulate the HASR with two quench flows. The mass balance, energy balance, and pressure drop equations have been solved simultaneously by fourth-order Runge–Kutta method using MATLAB software to obtain concentration, temperature, and pressure profiles along the reactor beds. For effectiveness factor calculation, a modified shooting method has been used to solve two point boundary value differential equations. The simulation results are compared with the plant data, and good agreement is achieved. In the following, a new configuration for HASR is proposed. The proposed design combines intercooled and two quench flow HASRs. Hence, comparing to the conventional HASR with two quench flows and intercooled HASR, it has higher nitrogen conversion and consequently higher ammonia production rate. The simulation results are compared with the conventional HASRs in order to demonstrate the improved performance of the proposed reactor.

Acknowledgment

The authors thank the cooperation of Khorasan Petrochemical Company for providing the ammonia plant data.

Symbols

aH2,aNH3,andaN2

[–]

Activity of hydrogen, ammonia, and nitrogen,respectively

A

[m2]

Cross-sectional area of beds

C

[kmol/m3]

Total concentration

Cpmix

[kcal/kg K]

Specific heat of gas mixture

Die

[m2/h]

Effective diffusion coefficient of component i

Di

[m2/h]

diffusion coefficient of component i

FN20

[kmol/h]

Initial molar flow rate of nitrogen

Ka

[–]

Equilibrium constant of reaction

k2

[–]

Reverse reaction rate constant

l

[m]

Bed length

m

[kg/h]

Mass flow rate

Mav

[kg/kmol]

Average molecular weight

Ni

[kmol/m2 h]

Molar flux of component i at catalyst particle

P

[atm]

Pressure

r

[m]

Radial coordinate of catalyst particle

Rg

[kJ/kmol K]

Universal gas constant

Rp

[m]

Equivalent radius of thecatalyst particle

RNH3

[kmol/m3 h]

Intrinsic rate of reaction

T

[K]

Temperature

u

[m/h]

Velocity

X

[–]

Conversion of nitrogen

yi

[–]

Mole fraction of component i

Greek symbols
ε

[m3/m3]

Porosity of catalyst bed

η

[–]

Effectiveness factor

ΔHr

[kJ/kmol]

Heat of reaction

μ

[Pa s]

Fluid viscosity

ρ

[kg/m3]

Density

θ

[–]

Intraparticle porosity

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Published Online: 2014-3-7
Published in Print: 2014-6-1

©2014 by Walter de Gruyter Berlin / Boston

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